Master unit for an intercommunication system



FIG. 1 is a front and right side perspective view of a master unit for an intercommunication system showing my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a top plan view thereof;

FIG. 4 is a right side elevational view thereof;

FIG. 5 is a left side elevational view thereof;

FIG. 6 is a rear elevational view thereof; and

FIG. 7 is a bottom plan view thereof. 

The ornamental design for a master unit for an intercommunication system, as shown. 